The application relates to a metering device for the volumetric metering of a pharmaceutical powder and filling of a plurality of target cavities with the metered powder, to a metering system, and to a method for metering such a powder using the metering device mentioned and for simultaneously filling a plurality of target cavities arranged in a common plane.
For the correct use of, for example, pharmaceutical powder by the target person, precisely metered partial quantities have to be provided, for example, in capsules, blister packs or other target cavities. First of all, volumetric metering of the powder is common for this purpose. The metered partial quantities are then poured into the target cavities.
If the target cavities are arranged in a row, use is commonly made of what are referred to as roller metering apparatuses. In this case, metering openings are provided on the circumferential surface of a metering roller along a line parallel to the longitudinal axis of the roller, said metering openings being filled with powder. The volume of the metering openings defines individual partial quantities of the powder, as a result of which volumetric metering is undertaken. The linear row of metering openings corresponds to the linear row of target cavities. After the metering openings have been filled, the metering roller is rotated until all of the metering openings lie above the target cavities. The volumetrically metered powder is then transferred out of the metering openings into the target cavities.
The metering and filling become problematic in particular whenever a relatively large number of target cavities which are not arranged in a line, but rather in a common plane, are intended to be filled simultaneously. This case occurs, for example, with what are referred to as DPI discs (dry powder inhaler discs), in which a plurality of target cavities, in particular 10 to 61 target cavities, are formed in a circular manner in a flat carrier disc and are surrounded by a seal surface. All of the target cavities in such a plane are intended to be filled simultaneously and are subsequently closed by sealing a sealing foil onto the seal surface. In such or comparable cases, the filling with roller metering apparatuses fails since the metering openings can be arranged only on an axially parallel line of the circumferential surface of the rollers and not in a plane. It would therefore only be possible simultaneously to fill two diametrically opposite target cavities. For the complete filling of all the target cavities lying in a plane, a plurality of sequential filling operations would therefore be required when a roller metering apparatus is used, and this is uneconomical.
One practicable way is the filling with what are referred to as pipettes although a correspondingly high number of individual pipettes is required with a correspondingly high outlay on investment. The use of pipettes is technically problematic in cases in which the target cavities have a non-circular basic outline. In addition, a sufficiently deep powder bed has to be provided, as a consequence of which an undesirably large residual quantity of powder cannot be avoided. Alternatively, use can be made of what are referred to as diaphragm metering apparatuses, in which the target cavities are covered with an air-permeable diaphragm. A powder channel is guided through the diaphragm. By applying a negative pressure difference to the diaphragm, powder is sucked into the target cavity through the powder channel and retained at the diaphragm. Apparatus and method are restricted to bringing about a filling of the target cavity to the edge. The connection of diaphragm and powder channel is technically problematic, with the effective diaphragm surface also being reduced by the cross section of the powder channel guided therethrough. The cross section of the powder channel therefore has to be selected to be as small as possible, but this opposes a reliable throughflow of the powder. Problems can also occur here in the filling of target cavities which are non-circular in basic outline if, in narrow basic outline regions, a sufficiently large space does not remain for the diaphragm on the other side of the powder channel.